Much of the central floodplain of the ancient Euphrates now lies beyond the frontiers of cultivation, a region of empty desolation. Tangled dunes, long-disused canal levees, and the rubble-strewn mounds of former settlement contribute only low, featureless relief.Vegetation is sparse, and in many areas it is almost wholly absent. Rough, wind-eroded land surfaces and periodically flooded depressions form an irregular patchwork in all directions, discouraging any but the most committed traveler.To suggest the immediate impact of human life there is only a rare tent... Yet at one time here lay the core, the heartland, the oldest urban, literate civilization in the world.(Robert McC. Adams, Heartland of Cities, Chicago, 1981)

Although energy economists might see price as the only barrier to utilization of a resource, scientists (including geologists) should place greater trust in the predictive value of the laws of thermodynamics.When the energy required for mining coal becomes greater than the energy obtained by subsequently burning it, then the mining will not occur -- no matter how high the coal price or how much coal remains in the ground. (Michael Lardelli, Science 324 (2009) p.880)